1. Field of the Invention
The present invention relates to a flow control valve for use in robots, etc. and, in particular, to a high-speed flow control valve having excellent high-speed response for medium to high pressures and capable of performing continuous control easily.
2. Description of the Related Art
As a flow control valve in which a piezoelectric body is used as a driving source, those disclosed in Japanese Patent Laid-Open Nos. 62-283273 and 62-283274 have been known. To explain these valves with reference to FIGS. 7 and 8, a flow control valve in the former patent is so arranged that a bimorph piezoelectric plate C3 having a valve seat C2 in the center inside a valve chest C1 is laterally installed, as shown in FIG. 7, and the opening and closing of a flow path is performed by making the above-mentioned valve seat C2 move closely to and separately from an air flow slot C4 disposed on the wall of the valve chest. As shown in FIG. 8, a flow control valve in the latter patent is so arranged that an arm D6 is disposed in such a manner as to be laterally placed inside a valve chest D1, and one end of this arm D6 is connected to a fixed fulcrum D4 and held in a cantilevered form. The front end of the arm D6 is capable of performing a flexing movement and a pair of air flow slots D7 opened in the valve chest D1 are disposed facing this flexing direction. A valve seat D3 having a spring D2 energized in the direction in which the air flow slots D7 are closed is disposed in the front end of the arm D6. An electrostrictive element D5 for forcedly providing a flexing movement to the arm D6 is disposed between fixation sections in the vicinity of the fulcrum D4 of the arm D6. As a result, the flexing movement is caused by amplifying the amount of the directly operated displacement .DELTA.x of the electrostrictive element D5 by means of the arm D6 so that the valve seat D3 is made to move closely to and separately from the air flow slots D7 disposed on the wall of the valve chest so as to open and close a flow path. It is considered that any of these flow control valves is convenient for use in pneumatic low-pressure oil flow control valves or the like.
However, when the above-mentioned conventional flow control valve is sued for medium to high pressures, there arises such drawbacks as described below.
(1) In the former flow control valve, flexing oscillation is caused in the piezoelectric plate C3 so as to open and close the valve seat C2 and the air flow slot C4 at high speed. Although this flow control valve can perform high-speed control easily as described above, since the opening and closing force of a valve at maximum is limited to approximately 100 g, there exists a difficulty in using the valve for medium to high pressures.
(2) In the latter flow control valve, there is a limitation in that the spring D2 must be one having a spring constant in the range not exerting an influence on the arm D6. For this reason, this valve is not suited as a flow control valve for medium to high pressures that requires a large spring constant. If it were used as a flow control valve for medium to high pressures that requires a large spring constant. If it were used as a flow control valve for medium to high pressures without modifications, since the spring constant is low, the displacement loss of a valve seat becomes larger because of the reaction force of fluid pressure and a drawback such that fluid control cannot be performed with high accuracy will arise.